1. Field of the Invention
The present invention relates to a color image forming device for forming color images, wherein carrying members for carrying developing agents of various colors are juxtaposed along a moving direction of an intermediate recording medium.
2. Description of the Related Art
There is known a color laser printer including a single photosensitive drum and an intermediate drum. A toner image is formed on the photosensitive drum, and then transferred onto the intermediate drum. The same operation is repeatedly performed for each of a plurality of different colors. As a result, visible toner images of different colors are overlaid in turn, thereby forming a color image on the intermediate drum. Then, the color image Is transferred onto a paper sheet. In this type of printer, however, the time required for forming a color image, for example a four-color image, would be four times that required to form a single-color image. Hence, it is difficult to form a color image at a high rate of speed.
There is also known a tandem color laser printer using a tandem image-forming method. This type of laser printer includes a plurality of developing units juxtaposed in a juxtaposing direction, such as vertical or horizontal direction. Each of the developing units stores different color toner, that is, one of cyan toner, magenta toner, yellow toner, and black toner, and includes a developing roller, a charging unit, and an exposing unit. The developing roller is for carrying the toner. The photosensitive drum is disposed opposite the developing roller. The charging unit and the exposing unit are disposed in opposition to the photosensitive drum for forming an electrostatic latent image thereon. A visible toner image corresponding to the electrostatic latent image is developed on the photosensitive drum and directly transferred onto a paper sheet which is being transferred in the juxtaposing direction of the developing units. As a result, toner images of different colors are overlaid In turn on the paper sheet, thereby forming a color image thereon. Because the plurality of developing units perform toner image developing operations nearly simultaneously, a color image can be formed on a paper sheet at an extremely rapid rate.
However, because toner images are directly transferred from the photosensitive drums onto the paper sheet in the tandem color printer, fluctuations in the resistance value on the paper sheet can make the toner images unstable and prevent proper transfer of the toner images. More specifically, the resistance value of the paper sheet can vary due to ambient humidity, thickness of the sheet, type of sheet material, and the like. This changes the charge retaining ability of the paper sheet. As a result, satisfactory toner image transfer may not be performed. Also, toner transferred at an upstream-side developing unit may be deposited on a photosensitive drum of a downstream-side developing unit with respect to the juxtaposing direction, thereby undesirably mixing the different colors and reducing image quality.
In order to overcome the above problems, there has been proposed a color image forming device in which a color image is once formed on an intermediate recording medium and then transferred from the intermediate recording medium onto a paper sheet. Because the resistance value of the intermediate recording medium is substantially fixed at all times, a high-quality color image can be formed.
In this case, however, a visible image is transferred two times, that is, once onto the intermediate recording medium and once onto the paper sheet. This double transfer can cause a marked decline in image quality if the toner has low transfer efficiency.
Also, when the photosensitive drum is replaced, a new photosensitive drum may be set slightly out of position. Also, during replacement of the photosensitive drum, it may be necessary to detach or move the charging unit or the exposing unit, or these units may be accidentally moved, so that the units may become out of alignment. In these cases, poorly registered color images and undesirable color mixing can occur, resulting in poor image quality.
In view of the foregoing, it is an objective of the present invention to overcome the above problems and to provide a tandem image forming device capable of forming high-quality color images at a high rate of speed without deterioration in image quality due to Image transfers.
In order to achieve the above and other objectives, the present invention provides a color image forming device including a plurality of electrostatic latent image bearing members, a plurality of charging units, a plurality of exposing units, a plurality of developing agent bearing members, and a plurality of layer regulating units. The electrostatic latent image bearing members are aligned in a predetermined direction and have a surface. The charge units are provided in confrontation with the corresponding electrostatic latent image bearing members. The charging units uniformly charge the surface of the electrostatic latent image bearing members. The exposing units selectively emit a light onto the surface of the corresponding electrostatic latent image bearing members which has been uniformly charged by the charging units, thereby forming electrostatic latent images on the electrostatic latent image bearing members. The developing agent bearing members are disposed in confrontation with the corresponding electrostatic latent image bearing members. The developing agent bearing members bear developing agent of different color. The layer regulating units regulate a thickness of a layer of developing agent on the corresponding developing agent bearing members into a two-layer thickness or less.
There is also provided an image forming device including a plurality of developing units for different color, an intermediate recording medium, a first transfer unit, a recording medium feeding unit, a second transfer unit a feeding direction changing unit. Each of the developing units includes a developing agent bearing member that bears a non-magnetic single component developing agent, an image bearing member, and an electrostatic latent image forming unit that forms an electrostatic latent image on the image bearing member. The developing agent bearing member selectively supplies the developing agent onto the image bearing member, thereby developing a visible image corresponding to the electrostatic latent image on the image bearing member. The first transfer unit transfers the visible images from the developing unit onto the intermediate recording medium, thereby forming a color image on the intermediate recording medium. The recording medium feeding unit feeds a recording medium in a feeding direction. The recording medium has a first surface and a second surface opposite the first surface. The second transfer unit transfers the color image from the intermediate recording medium onto the recording medium. The feeding direction changing unit changes the feeding direction. The feeding direction changing unit changes the feeding direction after the color image is formed on the first surface of the recording medium for forming a subsequent color image on the second surface of the recording medium.